Electrolytic cell



Oct. 23, 1956 S. L. ADELSON ELECTROLYTIC CELL.

Filed Aug. 4, 1955 IN V EN TOR.

United States Patent C) ELECTROLYTIC CELL Application August 4, 1953,Serial No. 372,308

6 Claims. (Cl. 204 359 This invention relates to electrolytic cells formeasuring electrieally-determinable characteristics of liquids, such asconductivity, 0. R. P. (oxidation-reduction potential),

pH (hydrogen ion concentration) various ion concentrations, or D. 0.(dissolved oxygen). More particularly, the invention is concerned withan improved through-flow cell of the type wherein the liquid whoseelectrically-determinable characteristic is to be measured is a part ofa closed pressure system.

It is an object of this invention to provide an improved electrolyticcell of the type including a noble metal electrode in direct contactwith the liquid sample whose characteristic is to be measured, and areference electrode, such as, for example, a calomel electrode, which isin ionic contact with the liquid sample through a salt bridge.

Another object is to provide in an electrolytic cell of this generaltype means to keep the noble metal electrode and the interface betweenthe salt bridge and the flowing liquid sample free of deposits.

Another object is to provide an improved electrolytic cell of thisgeneral type which is suitable for measuring anelectrically-determinable characteristic of a flowing liquid underpressure and necessitates a minimum of cleanmg.

Another object is to provide a through-flow electrolytic cell includingmeans for keeping a clean interface between the flowing liquid sampleand the salt bridge and preventing pollution of the salt bridge by theliquid sample.

Another object is to provide an electrolytic cell of this general typewherein means are provided to cause a slight, controlled flow or oozingof the electrolyte forming the salt bridge across the salt bridge-sampleinterface.

Other objects will become apparent upon consideration of the descriptionand of the claims which follow.

It is well known to measure characteristics of a liquid, such asconductivity, 0. R. P., pH, or D. 0., by means of electrolytic cells andto utilize the potential dilference or current developed by the cell forindicating and for controlling the value of the characteristic measured.For example, the potential or current can be applied to a controllerwhich actuates a feeder or a valve to provide the quantity of treatingagent needed in order to maintain the desired value of thecharacteristic.

It has long been recognized that, in order to obtain accurate readings,the electrodes of an electrolytic cell must be kept free of deposits offoreign matter and of films of slime or the like. Many expediencies havebeen proposed to avoid the necessity of frequent electrode cleaning,such as projecting abrasive material against the electrode surfaces.When dealing with liquid containing relatively large quantities ofsuspended and dissolved organic matter, it is not only important to keepthe electrodes clean, but it becomes also imperative to prevent depositsin all portions of the cell. Obviously, the decomposition of organicmatter deposited in any part of the cell will alter the composition ofthe liquid sample and prevent accurate measurements. To keep theelectrodes, as well 2,768,135 Patented Oct. 23, 1956 as the cell body,free of deposits, it has been suggested to provide through-flow cellsand to establish a flow through the cell of sufficient velocity tocontinuously sweep the contact areas of the electrodes and preventsettling in the through-flow passage. In the operation of suchthrough-flow cells it has been found that the usual gelatinous or fiberplug or wick, or other porous closure, constituting the interfacebetween the liquid sample and the salt bridge, is subject to thedeposition of organic films which interfere with exact readings and thusnecessitate frequent cleaning of the cell.

Such filming can be prevented by causing a small, controlled flow, inthe form of individual drops or oozing of the electrolyte forming thesalt bridge through the porous closure separating the salt bridge fromthe liquid sample. Alternatively, the porous closure may be replaced byan open-ended capillary tube to establish direct contact of theelectrolyte with the liquid sample, and a controlled flow can be inducedtherefrom.

To obtain a flow through the porous closure or from the capillary tube,I provide means in the through-flow conduit for reducing the pressure inthe vicinity of the closure or capillary tube to a value below that ofthe head of the electrolyte on the closure or capillary tube. Thereduced pressure at the point of liquid junction between the salt bridgeand the liquid in the through-flow conduit serves the double purpose ofcausing the flow of electrolyte which keeps the junction clean, and ofpreventing the liquid sample from entering the porous closure orcapillary tube and polluting the salt bridge.

The means for reducing the pressure may take a variety of forms and bebased on various flow principles or combinations of such principles.Thus, the flow area of the liquid sample may be reduced with resultantincrease in velocity, or the flow may be turned around a corner. Variousshaped bodies can be introduced in the flow stream with a pressurereduction occurring downstream thereof. A pressure decrease can also beobtained in a pump suction line or a siphon. Some means based on theseprinciples are shown in the drawings while others will become apparentto those skilled in the art upon consideration of the detaileddescription and the drawings, wherein similar elements are designated bythe same numerals.

Figure 1 is a diagrammatic vertical cross-sectional view of a cellaccording to the invention;

Figure 2 is a diagrammatic partial vertical cross-sectional view ofanother embodiment of the invention;

Figure 3 is a diagrammatic plan view of another embodiment of theinvention; and

Figure 4 is a diagrammatic partial vertical cross-sectional view ofstill another embodiment of the invention.

In the figures the liquid whose characteristic is to be determined flowsthrough a conduit 10 in the direction of the arrows. The conduit 10 ismade of non-conducting material, such as glass, or plastic material. Theliquid entering conduit 10 may be the entire flow through a treatingplant; ordinarily, however, a sample flow will be by-passed from themain flow through the inlet end of conduit 10 and may be returned to themain flow at any suitable part of the plant, or in some cases be sent towaste, through the outlet end of conduit 10.

An electrode 15, preferably of a noble metal, such as platinum or gold,has a surface in a section of conduit 10 of suitable length. As shown inFigures 1 to 3, the electrode 15 extends only partway around the innersurface of the conduit 10; however, if a larger surface area is desired,it may be extended around the entire inner surface, as shown in Figure4. The electrode 15 is shown for clarity as a plate, but it can be athin metal foil, or a metal film deposited on the inner surface of theconduit it) in known manner. A wire 16 extends from the outside throughthe wall of the conduit and is connected to the electrode 15. When thecell is in use, the wire 16 is connected in an electrical circuit withwire 17 which is connected to a reference electrode 20 of suitablematerial, such as calomel.

As shown in Figure l, the reference electrode 20 extends through a plug111 into a reservoir 22 which may be filled with potassium chloride orother electrolyte forming a salt bridge between the electrode 2%) andthe liquid flowing through the conduit 10. The reservoir 22 may be ofsufficient size to hold a large supply of electrolyte, or, as shown inFigure l, a supply tank 23 may be connected to the reservoir 22 by avalved pipe 24.

The salt bridge and the sample liquid communicate by means of acapillary connection 25, which may be a porous closure 25:: withnumerous minute openings, as shown in Figure 2, or, as shown in theother figures, a single capillary tube 251) open to the reservoir 22 andto the conduit it). In either case, the connection 25 will be located ina zone of reduced pressure so that a small flow of electrolyte throughthe capillary connection is induced, which will keep the interfacebetween the electrolyte and the liquid sample clean of films anddeposits. Further, the liquid sample, which may be under a higherpressure than the head of electrolyte over the capillary, is preventedfrom entering the capillary and polluting the salt bridge by the reducedpressure at the point of capillary connection. The small amount ofelectrolyte which is continuously exuded from the reservoir 22 throughthe capillary connection 25 can be replenished from the supply tank 23,to maintain a substantially constant liquid level in reservoir 22.

In Figure 1 the means for obtaining a reduced pressure are shown in theform of a venturi tube 30 inserted in the conduit 16*. The nobleelectrode preferably is installed upstream of the throat 31 of theventuri while the capillary connection 25 shown in the form of a tube25b opens to the venturi throat 31. The reduction in fluid pressure dueto the reduced flow area at the venturi throat 31 induces a slight flowof liquid from the capillary tube 25b into the conduit 10. In thismanner the liquid forming the junction between the salt bridge and theliquid sample is continuously renewed, and film formation and depositsare prevented.

In Figure 2 the liquid junction between the salt bridge and the flowingliquid sample is located on the suction side of a pump 35 installed on,or otherwise connected with, the conduit 19a. The conduit 10a may be ofany desired configuration. The inlet end of conduit 18a is submergedbelow the liquid level L of the tank or pit from which the liquid ispumped, and extends preferably to a higher elevation than the level L toprevent a pressure buildup in conduit 10a in case the pump 35accidentally fails to work.

In this embodiment the liquid in the reservoir 22 communicates with, andis exuded through, a porous plug or closure 25a, which may be agelatinous or fiber plug or the like; but it will be understood that acapillary tube, as shown in the other figures, could be used instead. Asthe pump 35 is operated, a small amount of electrolyte is oozed throughthe porous plug 25a into conduit 10a, whereby the surface of the plug iscontinuously washed and freed of deposits and films.

In Figure 3 the means for obtaining a reduced pressure comprises anelbow-shaped portion 49 in the conduit 10. The reservoir 22 is connectedto the elbow 40 by a capillary tube 25b, as shown. The electrode 15 maybe arranged just upstream of the junction of the capillary tube 25b withthe elbow 4d. The pressure reduction due to the liquid changing itsdirection of flow exudes a small flow from the capillary tube, so thatthe liquid junction etween the salt bridge and the flowing sample iscontinuously reformed by fresh electrolytic liquid.

Figure 4 shows still another means for obtaining a pressure reduction inthe vicinity of the point of ionic communication between the liquidsample and the electrolyte forming the salt bridge. In this figure thecapillary tube 25b and the surrounding tube in which the capillary issealed are extended into the conduit 10 in the direction of flow,whereby a reverse Pitot tube 45' is formed. The resultant pressurereduction in conduit 10 downstream of the tube 45 will suck a smallquantity of electrolyte from the capillary tube 25b and keep theinterface between the salt bridge and the flowing liquid sample clean.

While the above means for obtaining a pressure reduction have been shownand described for purposes of illustration in separate embodiments,several of these means can be combined with advantage in a singleinstallation. Thus, for example, when the pump 35 of Figure 2 is used,an additional reduction in pressure can be obtained by a slightrestriction of the conduit 10a in the vicinity of the porous closure25a. The same is true of the embodiment of Figure 4, where a slightrestriction of the conduit 10 around the reversed Pitot tube 45 willprovide an additional slight pressure reduction. Similarly, while theconduit of Figure 4 has been shown for purposes of exemplification as astraight tube, it could be in the form of an elbow, as shown in Figure3. Other combinations will be obvious to those skilled in the art. Thechoice of the particular means, or combination of means, for obtaining apressure reduction depends on the value of the reduction needed andother features of individual installations. Thus, where the liquidsample flow must be pumped, utilization of the pump suction, as inFigure 2, for obtaining the pressure reduction will be in order, whilein a gravity flow system the venturi of Figure 1 might be preferable.

While the noble metal electrode 15 has been shown in Figures 1 and 3 forpurposes of illustration upstream of the capillary connection betweenthe electrolyte forming the salt bridge and the liquid sample, it may belocated in the conduit just opposite the capillary connection, as shownin Figures 2 and 4 as the velocity in this vicinity is sufiicient toimmediately divert the small flow of electrolyte in downstreamdirection. Further, the noble metal electrode 15 need not form a part ofthe inner surface of the conduit 10, as shown in the drawings, but cantake any suitable shape as it is continuously washed by the liquidflowing through the conduit 14). This is particularly true if theelectrode 15 is installed in the area of reduced pressure and highvelocity flow.

It will be obvious to those skilled in the art that the electrolyticcell shown and described herein will be enclosed in a suitable casing,not shown, so that it may be installed as a unit.

Various modifications can be made without departing from the scope andspirit of the invention. Thus, the conduit 10 could be a siphon and thecapillary connection be located at its top. It will, therefore, beunderstood that I do not wish to limit myself to the exact structuralfeatures shown in the drawings for purposes of exemplification but notof limitation.

Iclaim:

1. An electrolytic cell for measuring an electricallydeterminablecharacteristic of a flowing liquid comprising a conduit for flow of theliquid whose characteristic is to be determined, a first electrodehaving a contact area in communication with the liquid flowing throughsaid conduit, .a second electrode, a body of electrolyte incommunication with said second electrode and also in ionic communicationwith the liquid flowing through said conduit, and means connecting saidelectrodes in an electrical circuit, characterized by means forcontinuously keeping said first electrode and the point of ioniccommunication between said body of electrolyte and the liquid flowingthrough said conduit free of deposits, said means comprising a deviceeffective to lower the pressure in a portion of said conduit below thehead of said body of electrolyte on said point of ionic communication,said first electrode and said point of ionic communication being locatedin the said portion of said conduit wherein the pressure is lowered.

2. The apparatus of claim 1 wherein said device effectivetglgwer thepressure is a venturi tube forming at least part of said conduit, saidfirst electrode is located within said venturi tube upstream of itsthroat and said point of ionic communication of said body of elecrtolytewith the liquid flowing through said conduit is at the throat of saidventuri tube.

3. The apparatus of claim 1 wherein said device eifective to lower thepressure comprises a pump installed on said conduit With its suctionside downstream of said first electrode and of said point of ioniccommunication.

4. The apparatus of claim 1 wherein said device effec tive to lower thepressure is an elbow section in said conduit, said first electrode isinstalled in said elbow section, and said body of electrolyte is inionic communication with the liquid flowing through said elbow.

5. The apparatus of claim 1 wherein said ionic communication comprises acapillary tube extended into said 20 conduit in the direction of flow,and said first electrode is located in said conduit in the zone ofreduced pressure created by said capillary tube.

6. In an electrolytic cell for determining an electricallydeterminablecharacteristic of a flowing liquid, said cell being of the through-flowtype and including a liquid flow conduit, a first electrode having acontact area adapted to be in communication with liquid flowing throughsaid conduit, a second electrode, a salt bridge in contact with saidsecond electrode and in ionic communication with liquid flowing throughsaid conduit, and means connecting said electrodes in an electricalcircuit, a venturi tube forming at least part of said conduit, saidionic communication comprising a capillary connection with the throat ofsaid venturi tube, said venturi tube being shaped to cause a sutficientreduction in pressure at said throat to induce a flow from said saltbridge through said capillary connection, said first electrode beingmounted in the zone of reduced pressure in said venturi tube.

References Cited in the file of this patent UNITED STATES PATENTS667,559 Neubauer Feb. 5, 1901 1,513,558 Parker Oct. 28, 1924 1,951,205Rather et a1 Mar. 13, 1934 2,219,616 Bradshaw et a1. Oct. 29, 19402,289,687 Stuart -a July 14, 1942 2,382,735 Marks Aug. 14, 1945

1. AN ELECTROLYTIC CELL FOR MEASURING AN ELECTRICALLYDETERMINABLECHARACTERISTIC OF A FLOWING LIQUID COMPRISING A CONDUIT FOR FLOW OF THELIQUID WHOSE CHARACTERISTIC IS TO BE DETERMINED, A FIEST ELECTRODEHAVING A CONTACT AREA IN COMMUNICATION WITH THE LIQUID FLOWING THROUGHSAID CONDUIT, A SECOND ELECTRODE, A BODY OF ELECTROLYTE IN COMMUNICATIONWITH SAID SECOND ELECTRODE AND ALSO IN IONIC COMMUNICATION WITH THELIQUID FLOWING THROUGH SAID CONDUIT, AND MEANS CONNECTING SAID ELECTODESIN AN ELECTRICAL CIRCUIT, CHARACTERIZED BY MEANS FOR CONTINUOUSLYKEEPING SAID FIRST ELECTRODE AND THE POINT OF IONIC COMMUNICATIONBETWEEN SAID BODY OF ELECTROLYTE AND THE LIQUID FLOWING THROUGH SAIDCONDUIT FREE OF DEPOSITS, SAID MEANS COMPRISING A DEVICCE EFFECTIVE TOLOWER THE PRESSURE IN A PORTION OF SAID CONDUIT BELOW THE HEAD OF SAIDBODY OF ELECTROLYTE ON SAID POINT OF IONIC COMMUNICATION, SAID FIRSTELECTRODE AND SAID POINT OF IONIC COMMUNICATION BEING LOCATED IN THESAID PORTION OF SAID CONDUIT WHEREIN THE PRESSURE IS LOWERED.